1. Field of the Invention
This invention relates generally to internal combustion engines, and more particularly to an observer for engine crankshaft torque. A related aspect of the invention involves a combustion pressure process model for the observer.
2. Background Information
An observer is a computational or numerical process that may be implemented in a digital microprocessor or in a digital signal processor. The observer acts on inputs supplied to it from various sources, such as sensors, to produce an estimate, or observation, of a variable of interest that, for any of various reasons such as cost or convenience of access, may be poorly suited for direct measurement. As such, observers are useful in multi-variable control systems as alternatives to direct measurement of at least some of the variables of interest. A closed-loop observer in which an observer feedback signal is compared to a measured quantity in order to force the other estimated quantities to converge to their actual, correct values, may provide a higher degree of performance than one that is not closed-loop.
Torque of a rotating shaft is one variable that may be considered relatively difficult to accurately measure, even in laboratory conditions. Hence it is believed to be well suited for estimation by an observer. Moreover, torque observation may eliminate the need for a devoted torque sensor, thereby improving robustness of a multi-variable system.
In an automotive vehicle powertrain, observation of the torque of an internal combustion engine crankshaft would be useful in the performance of various control functions related to powertrain operation, including for example engine control, transmission shift control, combustion diagnostics, and dynamometer testing. In a hybrid electric vehicle that has a starter/alternator associated with the engine, the electric machine can develop torque that can be independently controlled to interact with engine crankshaft torque in beneficial ways including: reduction of the ripple content of crankshaft torque, boosting transient crankshaft during vehicle launch and acceleration, recapturing breaking energy during vehicle decelerations, and retarding or boosting crankshaft torque for faster engine speed slewing during controlled shifting. Accurate observation of crankshaft torque in real time would be advantageous in controlling starter/alternator torque so as to secure its desired interaction with crankshaft torque in real time. Active control of the electric machine may enable it to function in a manner equivalent to a mechanical flywheel, and hence a starter/alternator that is controlled in this manner may sometimes be referred to as an active flywheel. An active flywheel may function to produce a zero mean value, destructively interfering torque that, when superimposed on the crankshaft torque, tends to reduce or eliminate ripple in the crankshaft torque caused by periodic combustion events in the engine cylinders.
In order to command the starter/alternator to produce correct torque for smoothing the ripple, precise instantaneous measurement of crankshaft torque during combustion events is needed. A crankshaft torque observer possessing this capability could be made an integral part of an overall fuel economy strategy for lowering engine idle speed while improving NVH (noise, vibration, harshness).
It is believed fair to state that combustion in internal combustion engines is a very complex and only partially understood process. More accurate modeling of the process is seen to be a desirable objective in advancing the state of the art because it should admit of more accurate torque observation.
A generic aspect of the present invention relates to an engine crankshaft torque observer comprising: a combustion process model for developing modeled estimates of combustion chamber pressures in engine cylinders according to certain engine inputs that influence combustion chamber pressures; a kinematics model for relating reciprocal motion of pistons in the engine cylinders to an engine crankshaft; an engine friction model for relating running friction of the engine to engine crankshaft rotation; and a processor for processing the certain engine inputs through the combustion process model to develop the modeled pressure estimates, for processing the modeled pressure estimates through the kinematics model to develop modeled positive torque contribution due to combustion processes, for processing the modeled pressure measurements through the friction model to develop modeled torque loss due to running friction, and for processing the modeled positive torque contribution due to combustion processes and the modeled torque loss due to running friction to develop an estimate of indicted torque output of the engine.
Another generic aspect relates to a method of engine crankshaft torque observation comprising: modeling an engine combustion process to develop modeled estimates of combustion chamber pressures in engine cylinders according to certain engine inputs that influence combustion chamber pressures; modeling engine kinematics relating reciprocal motion of pistons in the engine cylinders to an engine crankshaft; modeling engine friction relating running friction of the engine to engine crankshaft rotation; and processing the certain engine inputs through the combustion process model to develop the modeled pressure estimates, processing the modeled pressure estimates through the kinematics model to develop modeled positive torque contribution due to combustion processes, processing the modeled pressure estimates through the friction model to develop modeled torque loss due to running friction, and processing the modeled positive torque contribution due to combustion processes and the modeled torque loss due to running friction to develop an estimate of indicted torque output of the engine.
One related aspect of the invention concerns the combustion process model for developing modeled estimates of combustion chamber pressures in the engine cylinders according to certain engine inputs that influence combustion chamber pressures. Another related aspect concerns the method of modeling the engine combustion process.